This invention relates to the field of coupled data processing systems. More particularly, it relates to data processing systems operating independently but loosely coupled by attachment to a Structured External Storage (SES) processing facility.
Loosely coupled Data Processing systems in the past were often characterized by having more than one operating system (executing on different processors, or on a common partitioned processor) each attached to a shared direct access storage device (DASD) which contained shared data. In such systems the shared DASD functions as a mere repository--with each attached system (or program/process on such a system) manipulating data on the DASD, and other systems later viewing the results of such manipulation. IBM's MVS/SP JES2 provides an illustrative example of such an environment. In such an environment, the shared data repository (shared DASD) is a "passive" element, with the coupling being accomplished by means of protocols jointly agreed to among the systems, such as locking protocols, and, often, by direct communication between the systems.